Maximizing the Sum Rate of Massive MIMO with Rectangular Planar Array and MRT Beamforming

Abstract

We maximize the sum rate of maximum ratio transmission (MRT) beamforming in massive multiple input multiple output (MIMO) system, where the antenna configuration at the base station (BS) is uniform rectangular planar array (URPA). The sum rate maximization is performed by adopting a previous result concerning the channel inner product, which amounts to the orthogonality among user channels in a massive MIMO system. Different from the normalized channel inner product terminology, the channel inner product defined here assumes finite number of BS antennas. This assumption is necessary as we are interested in sum rate maximization by modifying the array dimension as the number of antenna elements is kept fixed. As MRT beamforming neglects any interference that might exists among user channels, the sum rate is thus maximized as long as orthogonality among user channels is preserved or the channel inner product is 0. We will also show that the maximum number of orthogonal channels is proportional to the largest dimension of the planar array. Hence, for a fixed number of antenna elements, reducing one of the array dimension creates more orthogonal user channels, and consecutively increases the sum rate.